Field of the Disclosure
The disclosure is directed to a hydraulic barrier and method of making the same. More particularly, the disclosure is directed to a hydraulic barrier containing polymer-clay granules and method of making the same, the hydraulic barrier being particularly suited for use in aggressive environments.
Brief Description of Related Technology
Hydraulic barriers are used in a number of industries for water absorption, containment, and/or retention. In a variety of industries, for example, the mining industry, the water source to be absorbed, contained, or retained is present in conditions that are incompatible with use of conventional clay-based barriers or even conventional clay and polymer dry mixtures containing barriers. Conventional barriers include, for example, geosynthetic clay liners, which have a layer of clay, such as bentonite clay, supported by a geotextile or a geomembrane material, mechanically held together by needling, stitching, or chemical adhesives.
Conventional barriers have shown to be ineffective or inefficient if the source has a high or low pH or contains a high concentration of soluble salts, and in particular divalent ions. It is commonly known that bentonite clay swells well in fresh water, but poorly in water having drastic pH conditions (pH<3 or pH>10) and/or containing salts and/or metals, such as saltwater, seawater, acid mining drainage, and the like. In such environments, it may be necessary to sufficiently prehydrate a conventional bentonite clay-based hydraulic barrier with fresh water prior to use, which can be burdensome and cost prohibitive in a variety of applications.
The hydraulic conductivity response of a granular bentonite-based GCL when exposed to a high pH leachate (pH>10) obtained from an aluminum leaching process has been investigated. The bauxite leachate had an ionic strength of 774 millimolar and a ratio of monovalent to multivalent cations (RMD)=1.15 M1/2, with Al and Na the predominant metals in solution. The hydraulic conductivity (K) of the GCLs was approximately 10−9 cm/s when permeated with tap water. When permeated with the highly caustic bauxite leachate, the granular bentonite based GCL became much more permeable, with a final hydraulic conductivity ranging between 4.2×10−7 cm/s and 1.8×10−6 cm/s.
Clay-polymer based hydraulic barriers such as those disclosed in U.S. Pat. No. 6,737,472 and U.S. Pat. No. 6,783,802 have been primarily developed with use of a water-absorbent polymer to facilitate and improve the retention of the clay within the hydraulic barrier mat material. For example, U.S. Pat. No. 6,783,802 describes a porous substrate, such as a geotextile liner having a polymerization initiator or polymerization catalyst embedded therein. The hydraulic barrier is formed by contacting this substrate with a monomer, cross-linking agent, and any other desired additives and subjecting it to conditions sufficient to polymerize the monomer within the substrate. The process results in improved retention of and embedding of the clay and polymer within the substrate material. In such a hydraulic barrier it can be preferable to have highly cross-linked polymers to ensure that the polymer remains retained and interlocked with the substrate during use. It was also believed that having such highly cross-linked polymers was necessary to ensure that the polymers were water insoluble and, therefore, would remain within the substrate during use.